Cooling Fans Running - Temperature Gauge not working - Yukon (and other models), my data, experience and rigged fix.

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The guitar zombie

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I am starting this thread because you have to go through a lot of posts to get where I am.

The problems (many models have it):


1) My 2015 Yukon Denali’s engine temperature gauge intermittently reads zero and the cooling fans come on where the computer assumes the sensor has failed so the car goes into a protective safe mode (fans run constantly - better too cool than too hot). if the Car is shut off with the fans running, they start up again when the car starts and will continue to run until 5 minutes after the car shuts off. The fans may, or may not start up the next time the car is started. It may run for a day or two and the problem will start up again.

2) The running fans cause problems.

a) the battery gets drained. On my Yukon, a near dead battery does not act typical to other older cars. Lights are bright, they don’t dim when heater is turned on, but when you hit the start button, the dash display goes black. Then the dash lights and headlights are bright again. Don’t be decieved, this is how a dead battery works (or doesn’t work) in a GM.

b) Because the control module doesn’t know the engine temp, the engine may not run properly. It may run rough or may be harder to start. Exhaust may be a bit more smelly.


Troubleshooting: I had my mechanic replace the engine temperature sensor. It worked, not because it needed one, but because he disconnected the battery and reconnected it. I took the old one and tested it. When the “old” sensor was immersed in three different cups of water (room temp 70°, ice cold 35° and hot 130° I measured the sensor’s resistance each time. It worked within spec (chart can be found on line). So my sensor wasn’t bad.

Opinions: many opinions and theories were offered in previous posts.
  1. The sensor itself is cheap and therefore intermittent. I am an engineering specialist with expertise in instrumentation and sensors. No. Not in this case.
  2. The wiring caused a power surge and killed the sensor. Again, no.
  3. One post even replaced the car’s computer ($$$) and still did not solve the problem.
  4. Loose connectors. I can’t say 100% no, but my mechanic did check the sensor’s connector.
Solution: This works but is not really a solution, but a work around. I added a battery switch. When I shut the car off, if the fan is running, I kill the battery via the switch (I bought and installed - there are many configurations). Every time, so far, the car starts normal (no fan running). There are systems you can buy that provide a switch near the dash. The cutoff can be an added safety feature as well. But, you will have to reset your date and time. Some of the car’s personal settings will have to be reprogrammed. The radio stations remain programmed though.

Suspicions: I think it is a control module programming issue.

Other thoughts - maybe rigging the control module fuse to have an in line switch on one of the terminals will reset the problem. I don’t know (yet) but next time, instead of disconnecting the battery, I will pull the fuse to see if it resets the temp sensing system. My guess is that it has the same effect (reprogramming) as disconnecting the battery cable, if it does the reset.

I will edit this post as I try different things.
 

mattbta

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The emissions monitors are going to be a PITA to complete if you have to get an obdii state inspection if you’re killing the battery every shutoff.
 

Fless

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Have you thought about reading the ECT sensor temp with a scanner to see what it's reporting? Then comparing that to actual (give or take) with an infrared temp gun?
 

HouTexTruckGuy

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I had the same problem with the Temp gauge stuck on zero and fans running, and no AC.

I changed out the ECT and it seems to have fix the problem and then it re-occured about a week later. I then used an OBD code reader and got the P0128 (Coolent Temperature Below Thermostat Regulating Temperature). I then used the OBD reader and erased the P0128 code reading. Everything went back to normal. We'll see if it lasts before troubleshooting further. I'm keeping the OBD reader in the vehicle because if the fan stays on too long, I check the see if the code is present. Erasing the code shuts the fans off immediately when the engine is not running.
 

Geotrash

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I had the same problem with the Temp gauge stuck on zero and fans running, and no AC.

I changed out the ECT and it seems to have fix the problem and then it re-occured about a week later. I then used an OBD code reader and got the P0128 (Coolent Temperature Below Thermostat Regulating Temperature). I then used the OBD reader and erased the P0128 code reading. Everything went back to normal. We'll see if it lasts before troubleshooting further. I'm keeping the OBD reader in the vehicle because if the fan stays on too long, I check the see if the code is present. Erasing the code shuts the fans off immediately when the engine is not running.
Boom! Guy stops in for one post and it's a winner!
 

L8T BURB

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Sorry to bump an old post, but I have the fix for this!!

I had this EXACT problem with my 2015 Suburban, and after extensive research online I realized there is not a lot of GOOD information on a true root cause/fix. I will include details of my repair journey which ultimately led me to the solution....

1. Replaced coolant temp sensor w/Autozone sensor (Temporarily seemed to correct the issue)
2. Replaced coolant temp sensor a 2nd time (Autozone warranty)
3. Replaced thermostat AND coolant temp sensor w/genuine GM parts (FIXED)

The only thing I can figure is that the factory thermostat was worn out and was leaking off (constantly staying partially open). This caused the engine temp to never get to normal operating range. This causes the vehicle to enter a "fail safe" mode, causing the fan to run non-stop (including several minutes after shut off), and also causes your AC system to not allow the AC compressor to engage.

If you run the engine long enough like this, you'll eventually get a check engine light and the code will read "operating temp below threshold". This means the engine is unable to get to normal operating range, and is fully entering the fail safe mode.

Trust me...I know it sounds far fetched to believe all these systems are tied together....but I assure you they are.

In short, grab a genuine GM thermostat housing as well as a genuine GM coolant temp sensor. You'll also need about a gallon of Dex-Cool. This repair is quick and easily can be done in your garage/driveway within 30 minutes with a couple of simple hand tools.

Hope this helps!!
 

zcb350fb

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hey interceptor589. do you have part numbers for those parts? I ran into this issue two days ago. replaced temperature sensor in auto zone parking lot because we were traveling. car ran great fro two days on the brand new sensor and then the issue resurfaced again today
 

Fless

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hey interceptor589. do you have part numbers for those parts? I ran into this issue two days ago. replaced temperature sensor in auto zone parking lot because we were traveling. car ran great fro two days on the brand new sensor and then the issue resurfaced again today

TIP o' the day: if you want to "tag" someone so they get notified, use either the "Reply" feature at the bottom of his/her post (like I did above), or start with the "@" sign, then start to type the username. A dropdown list will appear.

Like this:

1697593331948.png

Select the username from the dropdown -- @zcb350fb -- and continue writing your message. If you don't use either of those methods your target might not see your question.
 

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